1. Field of the Invention
The present invention relates to catheters, and more particularly, to catheter guide wire assemblies having a coiled wire wrapped round a core and safety wire.
2. Description of the Prior Art
Current techniques of introducing a catheter into the vascular system of a patient include the following steps: insertion of a sharp cannula through the skin and into the vascular system, insertion of a spring guide wire through the cannula and into the vascular system, removal of the cannula from the patient's body, and insertion of the catheter into the body by sliding the catheter over the guide wire. The guide wire is then withdrawn, and the catheter is ready for further positioning and use, or the guide wire can be left in position during use of the catheter.
It should be evident that the guide wire must be flexible and yet strong. It must be flexible enough to negotiate the desired tortuous path of the vascular system and do no damage with its leading tip portion and yet be strong enough to resist doubling back, kinking or breaking during the insertion and retraction procedures. It is accordingly desirable that the guide wire have a flexible and yet guidable distal tip, and a relatively stiff, strong elongated body portion. In addition to the foregoing, the guide wire should have an ultra-smooth outer surface.
A guide wire, sometimes referred to as a spring guide, is constructed of a finely wound spring with one or more wires running longitudinally within the spring's central lumen. A guide wire having a wound outer casing with an ultra-smooth surface, and an integral safety-core wire for ensuring structural integrity of the guide wire, without impairing guide wire flexibility at the distal tip, and a method of manufacturing such guide wire are described in U.S. Pat. No. 4,003,369, entitled "Angioplasty Guidewire With Safety Core Wire," the contents of which are herein incorporated by reference.
In one embodiment of the guide wire described in the referenced patent, the ultra-smooth outer surface of the wound guide wire is developed by coating a base flatwire with a lubricating agent, such as TEFLON synthetic resin, prior to being spring-wound about a core wire. In this manner, flaking of the outer coating is minimized during bending of the guide wire when in use. In another embodiment, the surface is smoothed by first lightly grinding the surface of the spring-wound flatwire by abrasion, and subsequently electropolishing the guide wire surface.
A safety-core extends longitudinally through the outer casing formed by the wound guide wire and is attached to the casing at the distal and proximal ends. The outer casing has a substantially uniform diameter throughout its entire length. The distal tip of the safety wire is made ultra-flexible in one direction by flattening a circular wire and immersing the wire into an electro-etching solution. Withdrawing the safety wire from the etch at a predetermined rate produces a uniformly tapered distal tip for the safety wire. In this manner, the transition between the ultra-flexible flattened distal tip and the relatively rigid circular body is smooth and uniform, having a carefully controlled cross-sectional area. Therefore, the possibility of breaking or kinking is minimized. That is, locations of preferential bending are eliminated.
For angioplasty or arterial dilatation, the guide wire is inserted into the blood vessel to be treated and a balloon catheter supported by the guide wire is positioned so that a distensible portion of the catheter is located in the stenosis to be treated. The catheter is then pressurized so that the distensible portion expands and compresses the stenosis. The balloon catheter is then deflated and the guide wire and catheter are pulled back from the portion of the blood vessel containing the stenosis so that a contrast medium used in a fluoroscopical procedure can be introduced into the blood vessel. Flow of the contrast medium through the region containing the stenosis is sensed to determine if the expanded stenosis has returned to its original restricted condition. If the dilatation procedure has not been successful, the guide wire must then be passed back through the stenosis a second time so that the dilatation procedure can be repeated. It should be appreciated that the reinsertion of the guide wire through the stenosis can be quite risky because of the just completed attempt to compress the stenosis. If it is necessary to repeat the process several times, the risk can become significant.